MXPA06004026A - Method and arrangement for friction welding - Google Patents

Abstract

The invention relates to a method and a device for friction welding, whereby one of the parts to be joined is oscillated by means of an electromagnetic oscillator. According to the invention, the oscillator is electrically braked after a regulated stimulation of oscillations and a pre-determinable oscillation period.

Description

METHOD AND DEVICE FOR PORTIFYING WELDING DESCRIPTION OF THE INVENTION The invention relates to a method and a device for friction welding in which one of the parts to be joined is oscillated with the help of an electromagnetic oscillator. To join parts by friction welding, heat is generated because the parts to be joined are rubbed against one another by pressing simultaneously against each other. This has the advantage that the heat is generated immediately in the areas to be joined together and that it is not necessary to transport it first through the parts to the welding point. An electromagnetic oscillator is provided to generate the friction heat, which is provided with a housing for one of the parts to be joined, while the other part is brought close and pressed against the first by means of a lifting table. To activate -eX 'oscillator, an alternating current is generated by a generator whose frequency corresponds to half the resonant frequency of the oscillator. Since this also depends on the housing for the workpiece in the oscillator, a frequency adjustment is required in known devices after a change of the housing for the workpiece. With regard to the foregoing, it is envisaged in a known device of EP 0 481 825 A2 that the working frequency of the generator is modified by a microprocessor until the current intensity. be minimal to a predetermined oscillation amplitude. However, there is a period in which the device does not work optimally. To improve this, it is additionally provided in the known device that the current curve that depends on the frequency is determined for a specific tool and stored in memory as a reference. In total it is not achieved with this, however, still a swing time as short as possible. The inventive method allows a short period of the welding process because the oscillator is braked after a regulated oscillation start and a predeterminable oscillation period. The inventive method is based on the discovery that the vibration is terminated as soon as possible after the joining operation, in order to avoid one of the already made joint. In addition, it is ensured by the controlled oscillation start that the resonance frequency is immediately adjusted completely automatically. This advantage takes a particular characteristic because the stimulation of oscillation and braking are carried out by alternating current under two electromagnets with opposite action because, depending on the respective direction of movement of the oscillator, an electromagnet that supports the movement is activated during the start of oscillation and an electromagnet that inhibits the-respective movement during braking, and because during braking, upon reaching a predetermined oscillation amplitude, the current is turned off. The shutdown of the energy upon reaching a predetermined oscillation amplitude avoids a new excitation with opposite phase position. The predetermined oscillation amplitude is selected in this way so that the junction point is not exposed to overload during the stimulation, now determined only by the mechanical damping. Depending on the specific conditions, the excited state can be maintained for a period that must be determined in each case. Particularly good results were obtained with the inventive method, when stimulation and braking; they are respectively shorter X than 80 ms. In an inventive device it is provided that an output of a displacement sensor that detects the respective position of the oscillator is connected to an input of a regulator whose output is connected to inputs of a power output stage for feeding the electromagnets. This device allows regulated stimulation in a particularly simple manner without there being a generator that first stimulates with a wrong frequency and that has to be synchronized later. Preferably, in the inventive device it is provided that the regulator controls the output stage in such a way that, depending on the respective direction of displacement of the oscillator, an electromagnet that supports the displacement is fed. By means of an improvement of this device, an advantageous execution of the braking process can be carried out because, for braking, an electromagnet is supplied which inhibits the respective displacement and the supply is switched off during braking upon reaching a predetermined oscillation amplitude. In this way, the stimulation transition, respectively, from the excited state to the braking can be effected in a simple manner by switching the power output stage. X An advantageous refinement of the inventive device consists in that the energy output stage consists of a first bridge branch of two semiconductor switches with two free-running diodes connected in parallel and two other bridge branches respectively comprising a connection in series of a semiconductor switch and a diode, in which the coils of the electromagnets are connected between the connection point of the semiconductor switches of the first bridge branch on one side and respectively a connection point of the additional bridge branches , that the semiconductor switches of the first bridge branch are stimulated with the oscillation frequency and the semiconductor switches of the additional bridge branches with pulse width modulation greater than the oscillation frequency or with tolerance band regulation, being -which can be presented higher frequencies than the oscillation frequency depending on the regulation status. Due to the losses that occur in each switching event in semiconductor switches and to avoid electromagnetic disturbances, it is tried to select the switching frequencies as low as possible. This is possible * with this conditioning X advantageously. Some semiconductor switches are switched with the oscillation frequency, for example 270 Hz, other semiconductor switches are switched several times per oscillation, with the switching frequency remaining in the area of few kHz. As a scanning frequency to detect the actual intensity and position values, an additional frequency of 15 kHz maximum is required. Although it is not necessary in this advantageous embodiment that all bridge leads be completely connected with semiconductor switches, it can be an advantage, due to economically available building modules, if the diodes are formed by semiconductor switches with running diodes free connected in parallel. Due to the higher frequency of commutations, the semiconductor switches in the other bridge branches absorb a greater load than those in the first bridge branch. In order to reduce this load it can be foreseen that the feeding of the electromagnets through the other bridge branches can be exchanged from one working cycle to another. Another advantageous refinement of the inventive device X consists in that means for generating activation for feeding the respective electromagnet are formed in such a way that the activation signal is present after a predeterminable fraction, preferably a quarter, of a period of oscillation after a step by zero of the oscillation.

In order to achieve a stimulation. As quickly as possible, the inventive device can be configured in such a way that the regulator comprises an integral activation component that is preloaded, in principle, with an essential value. Another embodiment of the inventive device consists of the oscillator including its elastic support and the housing for the workpiece, the displacement sensor, the regulator, the energy output stage and the electromagnets forming an oscillating circuit whose resonance frequency is essentially determined by the oscillator's own frequency including its elastic support and the housing for the workpiece. This also contributes to a rapid stimulation. Exemplary embodiments of the invention are represented in the drawing by several figures and are explained in detail in the subsequent description. This shows: ~ i Fig. 1 a schematic representation of an embodiment, Fig. 2 an energy output stage that can be used with particular advantage for the inventive device, Fig. 3 a time diagram for explaining the oscillation event and Fig. 4 a representation of the conduction phases of the semiconductor switches of the energy output stage. Fig. 1 shows the components of a friction welding device necessary to explain the invention. In a bridge 1 on the head, two electromagnets 2, 3 are arranged which attract an oscillating frame 4 according to their power supply respectively in the direction towards them - in the case of the electromagnet 2 in the direction of the arrow s. The oscillating frame 4 is supported on the head bridge 1 with the help of a spring 5 so that it can oscillate. The oscillating frame carries a housing 6 for the piece in process that is made in each case according to the part to be joined and which, correspondingly, can be exchanged. The oscillating frame 4, the spring 5 and the housing 6 for the workpiece are also referred to briefly as the oscillator. With the help of angles 7, 8, the head bridge is mounted on carriers 9, 10 forming part of the machine that carries, in a manner not shown, inter alia, a housing for the other part to be joined, which is pressed for the welding operation against the housing 6 for the workpiece in process. A displacement sensor 11 measures the respective position of the oscillating frame and transmits it as an electrical signal corresponding to a regulator 12. The output signals of the regulator 12 are fed to an energy output stage 13 which is connected in 14 in three-phase mode with the public network. An example for the power output stage 13 is shown in greater detail in Fig. 2. The public network current supplied at 14 is rectified by a three-phase rectifier. A capacitor 16 serves to homogenize the direct current as well as to buffer the pulsating load. The device shown in Fig. 2 is produced in large unit quantities as a three-phase voltage converter. A processor that is part of this and that is not shown in Fig. 2 only needs to be programmed in an appropriate manner for carrying out the invention. The energy output stage is formed by two transistors TI, T4, T3, T6 respectively; T5 T2 power connected in. they are connected in X parallel with respectively a diode DI, D4; D3, D6; D5, D2 free running. The derivation T3, T6 of bridge in between is regulated in each case as a function of the direction of displacement of the oscillator with the frequency of oscillation. To regulate the amplitude of the oscillation, the pulse width of respectively one of the transistors T5 or T4 is modulated with a higher frequency or according to a regulation of the current tolerance band. The diodes D3 respectively D6 of the bridge lead in the middle, as well as the diodes D2 and Di, serve here as free-running diodes. The details regarding the conduction phases of the semiconductor switches are explained below in relation to Fig. 4. Firstly, it is presented, however, the inventive method by means of Fig. 3. Diagram a shows the curve in the displacement time s of the oscillator, the diagrams d and c, the curve of the currents iL (2) and ÍL (3) of both electromagnets 2, 3 (Fig. 1). During the first three half waves, the electromagnets are fed in such a way that the oscillation is supported. During the third half wave, for example at the time ti, a braking command is performed, being that in the next half wave a waiting pause is formed because none of the electromagnets is powered. In the following half waves, starting at time t2, the same electromagnet is then fed, which brakes the oscillation, so that the amplitude decreases. As soon as the amplitude passes below a predetermined value 21, the current is turned off to prevent a further stimulation in the opposite phase. FIG. 4 shows a time diagram of the current i, as well as shaded areas, the respective conduction phases of the semiconductor switches. To power the electromagnet 2, the semiconductor switch T6 is conductive over most of the corresponding half wave of the displacement phase. During this period, the semiconductor switch T5 is regulated, wherein the scanning ratio is regulated according to the predetermined oscillation amplitude. Respectively after the semiconductor switch T5 is turned off, the current flows due to the energy accumulated in the running electromagnet -free through the diode D2 and the semiconductor switch T6. After turning off semiconductor switches T5 and T6 ', the current flows through diodes D2 and D3 back to the capacitor and rapidly extinguishes due to the voltage of this. The electromagnet 3 is fed into the next half wave. The driving phases of the switches T3 and T4 of semiconductor, '', as well as of diodes D6 and DI vf correspond to the conduction phases of semiconductor switches T6 and T5 as well as of diodes D3 and D2 in the preceding half wave.

Claims (12)

1. Method for friction welding in which one of the parts to be joined is put into oscillation with the help of an electromagnetic oscillator, characterized in that, after a regulated stimulation and a predeterminable oscillation time, the oscillator is braked electrically. Method according to claim 1, characterized in that the stimulation and braking are carried out by means of an alternating supply with a current of two electromagnets with opposite action, because, as a function of the respective direction of displacement of the oscillator, an electromagnet is supplied with current. the movement during the stimulation and an electromagnet that inhibits the respective movement during braking and because during braking the power supply is turned off when reaching a predetermined oscillation amplitude. Method according to one of the preceding claims, characterized in that the stimulation and braking is in each case shorter than '80 ms. 4. Device for friction welding in which an oscillator is being provided with which one of the parts to be joined is put into oscillation and which is driven by electromagnets of opposite action, characterized in that a displacement sensor output that detects the respective position of the oscillator is connected to the input of a regulator whose output is connected to inputs of a power output stage for supplying power to the electromagnets. Device according to claim 4, characterized in that the regulator controls the energy output stage in such a way that an electromagnet with current supporting the movement is fed as a function of the respective direction of movement of the oscillator. Device according to one of claims 4 or 5, characterized in that, in order to brake, an electromagnet is supplied with a current that inhibits the respective movement and because during braking, upon reaching a predetermined oscillation amplitude, the power supply is switched off with current . Device according to one of claims 4 to 6, characterized in that the energy output stage is formed by a first and bypass bridge consisting of two semiconductor switches connected in series with free-running diodes connected in parallel and two others. bridge branches consisting respectively of a series connection of a semiconductor switch and a diode, because the windings of the electromagnets are connected between the connection point of the semiconductor switches of the first bridge branch on one side and respectively a point for connection of the other bridge branches, because the semiconductor switches of the first bridge branch are controlled with the oscillation frequency and the semiconductor switches of the other bridge branches with pulse amplitude modulation or tolerance band regulation , being that higher frequencies can be produced than The oscillation frequency depends on the regulation status. Device according to claim 7, characterized in that the diodes are formed by semiconductor switches with free-running diodes connected in parallel. Device according to claim 8, characterized in that the power supply of the electromagnet is exchanged through the other bridge branches from the work cycle to the work cycle. 10. Device according to one of the claims 4 to 9, characterized in that means are shaped in such a way as to form an activation signal for the current supply of the respective electromagnet, that the activation signal is presented for a predeterminable fraction, preferably a quarter of a period of oscillation after a step by zero of the oscillation. Device according to one of claims 4 to 10, characterized in that the regulator has an integral activation component which is initially preset to an essential value. Device according to one of claims 4 to 11, characterized in that the oscillator including the elastic support and the housing for the workpiece, the displacement sensor, the regulator, the energy output stage and the electromagnets form an oscillating circuit whose resonance frequency is essentially determined by the frequency, own oscillator including the elastic support of this and the housing for the piece in process.